A momentous leap in green energy was made today as the California Energy Commission voted on a bill requiring all new homes to have solar, starting by 2020. This news is startling to say the least and to put things into perspective—California just became the first and only state to mandate rooftop solar panels on new home construction.

Solar panel costs are low and slipping ever lower. That means rooftop solar will become increasingly easy for the average person to adopt, and increasingly economically advantageous.

Green Tech Media reported in February that solar had reached grid parity – the point at which installing rooftop solar panels makes equal or better economic sense than traditional fossil fuel and coal-powered electricity generation – in 20 of the 50 states. GTM predicts that solar will be at grid parity in 42 states by 2020, just a little more than three years from now.